In most SEL relays, there are two different ways to measure ground fault current. One way (SEL relay word 50N) uses the current as measured by a core-balance CT physically wired to the In terminals. The other (50G) uses the mathematical summation of the three phase CT's.
My question is this...
Unless I am mistaken, typical trip circuits (125VDC) have a trip coil with a 52a contact on EACH side of the coil. Recently, I came across a design with a two 52a contacts in series on the positive side of the trip coil, and the trip coil itself was connected directly to the negative DC supply...
I'm trying to reduce tripping time to reduce incident energy levels as part of my arc-flash study. I have a Digitrip RMS310 (MES3800LSG). Is there a way to change the I2t characteristic of this device's operating curve without replacing the whole trip unit?
Can anyone inform me as to what the differences are between current limiting fuse type L and RK1s? IEEE1584 has different arc flash calculation parameters for each of these different types.
Any ideas why?
